The present invention relates to a method and device for determining the heading with wind (or with current) of an air (or sea-going) vehicle, from the heading without wind, usually called "course", and from a corrective value representative of the ratio between the wind (or current) speed and the vehicle speed.
Subsidiarly the invention proposes means for further determining an estimated time, with wind (or with current), which the vehicle will take to travel a distance between two geographical points, from an estimated time without wind (or without current).
First of all, it should be recalled that the heading without wind (or without current) is the heading which the vehicle would follow in the absence of wind (or current). To be able to cover the same route in the presence of wind (or current), the vehicle must make a drift correction and follow a fictitious heading called heading with wind (or with current). The estimated time without wind (or without current), once corrected as a function of the wind (or of the current), gives the estimated time with wind (or with current).
Traditionally, the heading and the time with wind (or with current) is determined either by means of a mental calculation, or a geometrical construction, or the use of an abacus or pocket calculator. It has proved however that these methods, which must often be applied by the pilot during piloting, are particularly inconvenient. They result in a work load, rely usually on manipulations and comprise risks of error.
The purpose of the invention is more particularly to reduce these drawbacks by simplifying said determinations to a maximum.
It is based on the discovery that drift and estimated time corrections are made by vectorial compositions in which the angles do not depend on the absolute value of the vectorial magnitudes but on their relative value, each magnitude being divided by the speed of the vehicle (speed with respect to the air or with respect to the current).
This property brings out the ratio between the wind (or current) speed and the vehicle speed, which ratio makes it possible to define a situation of the vehicle to which a given drift correction corresponds, for each relative position of the vehicle and of the wind (or of the current).
From the value of this ratio, the situation of the vehicle may be determined using a correspondence table or even an abacus having as coordinates the successive values of the vehicle speed and of the wind (or of the current) speed and a series of curves each indicating a preestablished situation of the vehicle.
Because the speed of the wind (or of the current) can be known from meteorological information or sea charts, and the vehicle speed is known, this determination may be made just before the flight (or the sea journey) or during the flight (or the sea journey).
Once the choice of the situation has been determined, the drift correction depends on the relative position of the heading without wind (or without current) of the vehicle and of the direction of the wind (or of the current), and only on that: a drift correction and only one corresponds to a relative position.
The Applicant has demonstrated that it was possible, to avoid calculating the heading with wind (or with current), by adding to the heading without wind (or without current) the drift correction, to use a correspondence system associating with a heading without wind (or without current) a heading with wind (or with current), without explaining the correction.